Circuits for electric discharge devices



Jan. 19,1932. 7 J S|V|AN 1,841,501

CIRCUITS FOR ELECTRIC DISCHARGE DEVICES Original Filed Dec. 5, 1923 I Afar/76y Y E UNITED STATES PAT N F JE.

J. SIVIAN, F" BLOOMFIELD, NEW JERSEY, ASSIGNOR TO TESTER/N ELECTRIC Patented 'Jan. 19,1932

GOMSEANY, INCORPORATED, OFNEW YORK, N. Y., A CORPORATION OFNEW'YORK CIRCUITS FORY ELECTRIO DISCHARGE DEVICES original.applicationifiled Decemberfi, 1923, Serial no. 678,650. Divided and this application November 23, 1926.

f This invention relates to circuits employi ing electric-discharge devices, particularly tively amplify signaling waves without the production of oscillations or singing.

Am lifying or other circuits employing electric discharge devices particularly those adapted for transmitting, high frequency waves have a tendency to oscillate due to the capacity coupling between the grid and plate of the device. This tendency is particularly noticeable i'namplifiers employing tuned circuits in bothrthe input and output circuits ofthe discharge device. When these circuits are ,bothtuned to the frequency of the waves tob'e amplified, both the'inputiand output circuits willhave a high inductive reactance at a frequency near the resonant point and theeffect of the internal capacity between grid and plate is to form an oscillating circuitrof the Hartleytype. f

In accordance with a feature of this invention the production of oscillations is preventedby providing ineither the input or output circuit a capacity reactive element to givethat circuit a capacity reactance. This effectively prevents the production ofoscillations,

since, the circuit will not oscillate when the This invention will be more readilyunder stood by reference to the following detailed description in connectionwith the drawings in which: Fig. 1' shows a radio receiving system employing an intermediate [frequency amplifier, constructed in accordance with this invention; and Fig. 2 shows amodification of i g J is to introduce a capacityreactance intotlie output-circuit of tube 59 in orderito prevent the. intermediate frequency amplifier of ing heterodyne oscillations.

filed Serial No. 150,193 N Fig. 1 shows a receiving system employing an antenna which isconnected to ground through an inductance 41 in series with a variable condenser 42. A detector 43 has its input circuit coupled to the antenna by means of an inductance-44 coupled to inductance 41 and forming a portion of-a resonant circuit 46. The remaining portion of the resonant circuit 46 comprises a variable condenser 47; A battery 48 is connected in the input circuit of detector tube 49 for supplying'a biasing potential toits grid. 7 p

The output circuit of detector 43 which comprises a connection between the filament and plate of tube 49 includes a resonant cir cuit 51 consisting of a variable condenseri52 i and an inductance 53. This resonant circuit is connected in series with a feedback coil 54 and a plate battery 56. The coil 54 is coupled to the inductances 41 and 44, whereby energy may be fed back from the output circuit to the input circuit of detector 43 for establishcircuitr46 maybe tuned to any desired frequency by adjusting the variable condenser 47. The resonant circuit 51 may likewise be tuned by adjusting the condenser 52. d

An intermediate frequency amplifier 57 is arranged to amplify energy from the detec tor 43. This amplifier has a resonant circuit 58 connected in its input circuit between the grid and filament of the vacuum tube 59 and the resonant circuit 58 has a coil 60 induc; tively coupled to the coil '53 of the res'onant circuit 51. The other element of the resonant circuit 58 consists of a variable con denser'fil. A grid biasing battery 62 is connected in the input circuit of tube 59 in series with the resonant circuit 58. The output circuit of the amplifier 57 includes a resonant i circu t 63 which comprises anlnductance' coil 6'? and a variable condenser 68. Abat-tery tube'59. Connected in series with the reso- The function of the variable condenser 64 The resonant '66is arranged tosupply platecurrent to the I the establishment of parasitic oscillations in the amplifier circuit, due to the capacity between the grid and plate, as indicated by dotted lines. The condenser 64 has preferably a range of capacity such that its effect upon the tuning of the amplifier is negligible and thus the selectivity of the circuit is unaffected thereby.

The impedance 65 is shunted around the condenser 64 to provide a path for direct cur rent from battery 66. This impedance may consist of an inductance and a resistance in series. v

A second detector 69 receives energy from amplifier 57. This detector comprises a vacuum tube 70 having an input circuit connected between its grid and filament. In this input circuit is a resonant circuit 71 coupled to the resonant circuit 63 and consisting of an inductance 72 and a variable condenser 73. The output circuit of detector 69 is connected between the filament and plate of tube 7 O and includes a receiver 74 shunted by variable condenser 75 and connected in series with a plate battery 7 6.

"In the operation of the receiving system of Fig. 1 energy of substantially constant amplitude having frequency modulation in accordance with signals or of substantially constant frequency but having amplitude modulations is received by antenna 4E0. This energy is transmitted through the coupled inductances 41 and 4st to tuned circuit 16 and from there to the input circuit of detector 413. The tuned circuit 16 is adjusted to resonance at the carrier or normal frequency of received waves. By means of the eedback coil 54 which couples the output circuit of detector 13 to its input circuit oscillations are established in the detector. These oscillations may be adjusted to have any desired frequency but are preferably made other than the frequency of received waves. Therefore, the incoming energy will combine with these oscillations in the input circuit of tube 49 and produce in the output circuit of this tube currents of frequencies which comprise the sum and difference of the received frequencies and the oscillation frequency. Tuned circuit 51 is adjusted to resonance at the desired intermediate frequency represented either by the sum or difference of the carrier and locally generated oscillations.

Energy of this intermediate frequency is supplied to amplifier 57 through the inductively coupled coils 53 and 60 of resonant circuit-s 51 and 58. The resonant circuits 58 and 63 in the input and output circuits, respectively, of amplifier 57 are tuned to the intermediate frequency.

In order to prevent parasitic oscillations or singing in this amplifier which may otherwise be established by virtue of the coupling between its output and input circuits supplied by the inherent capacity between the grid and plate as indicated in the dotted lines a condenser 64 is provided whereby the reactance of the output circuit may be adjusted in value and if desired may be caused to be in the nature of a capacity reactance. By adjusting condenser 64: the effective reactance of the output circuit may be caused to be of sign different from the sign of the effective reactance of the input circuit at any frequency at which oscillations tend to occur and the establishment of parasitic oscillations is prevented.- The impedance 65, is shunted about condenser 64 to supply a path for space current from battery 66.

Amplified energy of be intermediate fre-. quency is supplied to the second detector 69 by the coupling between coils 67 and 72 of resonant circuits 63 and 71. Resonant circuit 71 is tuned to the frequency represented in value approximately by the sum or difference of the intermediate frequency and the mean of the range of frequencies produced by the signal variations in the transmitter. On account of the form of the current-frequency characteristic of the resonant circuit 71, frequency variations in the energy supplied thereto produce corresponding amplitude variations in the potentials applied to the grid of detector tube 70. Thus, there results in the output circuit variations of current corresponding to signals as is well understood and these currents actuate the receiver 74. By the action of this detector which is now well understood, varying currents corresponding to the variations of signals are produced in its output circuit and actuate the receiver 7 4: connected therein.

In Fig. 2 a modification of the intermediate frequency amplifier 57 is illustrated. This circuit is identical with the corresponding one shown in Fig. 1 with the exception that condenser 64 together with its shunt impedance 65 is connected in the input circuit instead of the output circuit of the amplifier. By this arrangement the phase and reactance of the input circuit are adjusted relative to that of the output circuit for the purpose of preventing parasitic oscillations. The impedance 65 in this instance is preferably a resistance to supply a leak path for negative charges which would otherwise accumulate upon the grid of tube 59 and block its action. No further description of this figure will be given inasmuch as its operation is substantially identical with that of the amplifier 57 of Fig. 1.

WVhat is claimed is:

1. In combination an electric discharge device having input and output, electrodes, an input circuit connected to said input electrodes an output circuit connected to said output electrodes, the impedance-of each of said circuits having an inductive component at one frequency whereby the capacity coupling between the electrodes of said device tends to produce oscillations, and capacity means connected to form a series circuit with one of said circuits and the corresponding electrodes of said device for reducing the inductive reaction of said circuit to prevent said oscillations. I

2. An amplifier comprising a three-electrode electric discharge device, an input circuit connected to two of said electrodes, a resonant network in said input circuit, an output circuit connected between one of said first mentioned electrodes and a thirdfelectrode, a resonant network in said output circuit whereby the capacity coupling between the electrodes of said device tend to produce oscillations, and capacity means connected in one of said circuits to form a series circuit with the corresponding resonant network and electrodes of said discharge device for imparting a substantially capacity reactance to said circuit to prevent the establishment of said oscillations in said amplifier.

3. An amplifier comprising an electric discharge device, input and output circuits therefor, tuned coupling circuits in said input and output circuits, andcapacity reactive means connected in series with one of said tuned circuits for adjusting the relative phase of currents in said input and output circuits 1 to prevent oscillations.

4. An amplifier comprising a three-electrode electric discharge device, input and output circuits therefor, parallel resonant coupling networks in said input and output circuits, and a capacity impedance element connected in series with the parallel resonant network in one of said circuits to prevent parasitic oscillations due to the inherent capacity between the electrodes of said device. v I

5. An amplifier adapted to selectively transmit waves in substantially the same form as they are received comprising an electric discharge device, an input circuit therefor including selective means for impressing waves to be amplified upon said device, an output circuit including selective means for transmitting the amplified waves to a load circuit, and capacity means connected in one of said circuits in series with the respective selective means and having such capacity as to impart a substantially capacity reactance to said circuit to prevent ,theestablishment of oscillations in theamplifier.

In witness whereof, I hereunto subscribe my name'this 12th day of November A. D., 1926. i c

LEON J. SIVIAN. 

